diff --git a/src/inc/til/u8u16convert.h b/src/inc/til/u8u16convert.h
index 83f5dce0fc5..e84376f08b5 100644
--- a/src/inc/til/u8u16convert.h
+++ b/src/inc/til/u8u16convert.h
@@ -84,8 +84,8 @@ namespace til // Terminal Implementation Library. Also: "Today I Learned"
                 if ((*backIter & _Utf8BitMasks::MaskAsciiByte) > _Utf8BitMasks::IsAsciiByte)
                 {
                     // Check only up to 3 last bytes, if no Lead Byte was found then the byte before must be the Lead Byte and no partials are in the string
-                    const size_t stopLen{ std::min(in.length(), gsl::narrow_cast<size_t>(4u)) };
-                    for (size_t sequenceLen{ 1u }; sequenceLen < stopLen; ++sequenceLen, --backIter)
+                    const size_t stopLen{ std::min(in.length(), gsl::narrow_cast<size_t>(3u)) };
+                    for (size_t sequenceLen{ 1u }; sequenceLen <= stopLen; ++sequenceLen, --backIter)
                     {
                         // If Lead Byte found
                         if ((*backIter & _Utf8BitMasks::MaskContinuationByte) > _Utf8BitMasks::IsContinuationByte)
diff --git a/src/til/ut_til/u8u16convertTests.cpp b/src/til/ut_til/u8u16convertTests.cpp
index 93d46c9422a..105c657e3b0 100644
--- a/src/til/ut_til/u8u16convertTests.cpp
+++ b/src/til/ut_til/u8u16convertTests.cpp
@@ -83,31 +83,55 @@ void Utf8Utf16ConvertTests::TestU8ToU16Partials()
         '\xA4',
         '\xBD',
         '\x9C',
-        '\xF0' // CJK UNIFIED IDEOGRAPH-24F5C (lead byte only)
+        '\xF0', // CJK UNIFIED IDEOGRAPH-24F5C (lead byte + 2 complementary bytes)
+        '\xA4',
+        '\xBD'
     };
 
     const std::string u8String2{
-        '\xA4', // CJK UNIFIED IDEOGRAPH-24F5C (complementary bytes)
-        '\xBD',
-        '\x9C'
+        '\x9C' // CJK UNIFIED IDEOGRAPH-24F5C (last complementary byte)
     };
 
-    const std::wstring u16StringComp{
+    const std::wstring u16StringComp1{
         gsl::narrow_cast<wchar_t>(0xD853), // CJK UNIFIED IDEOGRAPH-24F5C (surrogate pair)
         gsl::narrow_cast<wchar_t>(0xDF5C)
     };
 
+    // GH#4673
+    const std::string u8String3{
+        '\xE2' // WHITE SMILING FACE (lead byte)
+    };
+
+    const std::string u8String4{
+        '\x98', // WHITE SMILING FACE (complementary bytes)
+        '\xBA'
+    };
+
+    const std::wstring u16StringComp2{
+        gsl::narrow_cast<wchar_t>(0x263A) // WHITE SMILING FACE
+    };
+
     til::u8state state{};
 
     std::wstring u16Out1{};
     const HRESULT hRes1{ til::u8u16(u8String1, u16Out1, state) };
     VERIFY_ARE_EQUAL(S_OK, hRes1);
-    VERIFY_ARE_EQUAL(u16StringComp, u16Out1);
+    VERIFY_ARE_EQUAL(u16StringComp1, u16Out1);
 
     std::wstring u16Out2{};
     const HRESULT hRes2{ til::u8u16(u8String2, u16Out2, state) };
     VERIFY_ARE_EQUAL(S_OK, hRes2);
-    VERIFY_ARE_EQUAL(u16StringComp, u16Out2);
+    VERIFY_ARE_EQUAL(u16StringComp1, u16Out2);
+
+    std::wstring u16Out3{};
+    const HRESULT hRes3{ til::u8u16(u8String3, u16Out3, state) };
+    VERIFY_ARE_EQUAL(S_OK, hRes3);
+    VERIFY_ARE_EQUAL(std::wstring{}, u16Out3);
+
+    std::wstring u16Out4{};
+    const HRESULT hRes4{ til::u8u16(u8String4, u16Out4, state) };
+    VERIFY_ARE_EQUAL(S_OK, hRes4);
+    VERIFY_ARE_EQUAL(u16StringComp2, u16Out4);
 }
 
 void Utf8Utf16ConvertTests::TestU16ToU8Partials()